Electrolytes For Energy Storage Devices Research Articles

Fluorinated Linkers Enable High-Voltage Pyrrolidinium-based Dicationic Ionic Liquid Electrolytes.

Novel fluorinated, pyrrolidinium-based dicationic ionic liquids (FDILs) as high-performance electrolytes in energy storage devices have been prepared, displaying unprecedented electrochemical stabilities (up to 7 V); thermal stability (up to 370 °C) and ion transport (up to 1.45 mS cm‑1). FDILs were designed with a fluorinated ether linker and paired with TFSI/FSI counterions. To comprehensively asess the impact of the fluorinated spacer on their electrochemical, thermal, and physico-chemical properties, a comparison with their non-fluorinated counterparts was conducted. With a specific focus on their application as electrolytes in next-generation high-voltage lithium-ion batteries, the impact of the Li-salt on the characteristics of dicationic ILs was systematically evaluated. The incorporation of a fluorinated linker demonstrates significantly superior properties compared to their non-fluorinated counterparts, presenting a promising alternative towards next-generation high-voltage energy storage systems.

The Interactions between Ionic Liquids and Lithium Polysulfides in Lithium-Sulfur Batteries: A Systematic Density Functional Theory Study.

Ionic liquids (ILs) based on hybrid anions have recently garnered attention as beguiling alternative electrolytes for energy storage devices. This attention stems from the potential of these asymmetric anions to reduce the melting point of ILs and impede the crystallization of ILs. Furthermore, they uphold the advantages associated with their more conventional symmetric counterparts. In this study, we employed dispersion-corrected density functional theory (DFT-D) calculations to scrutinize the interplay between two hybrid anions found in ionic liquids [FTFSA]- and [MCTFSA]- and the [C4mpyr]+ cation, as well as in lithium polysulfides in lithium-sulfur batteries. For comparison, we also examined the corresponding ILs containing symmetric anions, [TFSA]- and [FSA]-. We found that the hybrid anion [MCTFSA]- and its ionic liquid exhibited exceptional stability and interaction strength. Additionally, our investigation unveiled a remarkably consistent interaction between ionic liquids (ILs) and anions with lithium polysulfides (and S8) during the transition from octathiocane (S8) to the liquid long-chain Li2Sn (4 ≤ n ≤ 8). This contrasts with the gradual alignment observed between cations and lithium polysulfides during the intermediate state from Li2S4 to the solid short-chain Li2S2 and Li2S1. We thoroughly analyzed the interaction mechanism of ionic liquids composed of different symmetry anions and their interactions with lithium polysulfides.

Molecular insight into sequence-defined polyelectrolytes for energy storage devices

Polyelectrolyte (PE) adsorption on charged surfaces is a complex phenomenon that has an array of applications ranging from healthcare to designing energy storage devices. PE adsorption on surfaces involves surface charge polarization effects which arise due to the dielectric dissimilarities between the PE and the charged surface. PEs owing to their high potential window, and leakage-resistant behavior are used as supercapacitor electrolytes. Recent experimental evidence suggests co-block polymers as potential design materials for energy storage devices (ESDs). It is imperative to mention that the structural variation of the co-block polymers under spatial confinements will have a key role in designing electrodes and electrolytes for ESDs which demands a detailed investigation. This study reveals that the spatial orientations of the charged groups have an impressive impact on the changes in PE charge density peaks, charge amplification peaks, PE adsorption, counter-ion adsorption, and differential and integral capacitance while confined by graphene electrodes. It is startling to observe that the counter-ion distribution within the electrical double layer of the positively charged surface significantly depends on the orientation of the PEs. However, with increasing solvent dielectric constant the variations in the above-mentioned properties subside due to reduced electrostatic interactions. The differential capacitance and the integral capacitance are also found to be dependent on the dielectric constants of the solvent. These findings will be immensely useful in determining the key factors needed to describe the preferred spatial configuration of a PE suitable for various ESDs and applications involving PEs in a confined system.

Studies of the Properties of New Electrospun Based on PVA-PEG Polymer Systems Electrolytes for Energy Storage Devices

Solid polymer electrolytes (SPEs) have been considerably investigated due to various electrochemical device applications. Most of the SPEs comprise polymer as a host material to provide strength and good mechanical stability and salt that transfers charge carriers to cause conductivity. Nanocomposite solid polymer electrolyte membranes based on poly(vinyl alcohol) (PVA)-poly(ethylene glycol) (PEG) blend complexed with LiClO4 and nanofillers Al2O3 at different weight percent ratios have been obtained by using electrospinning method. The conductivity and structural properties of the different systems have been characterized by using various experimental approaches such as X-ray diffraction (XRD) and Fourier transform infrared FTIR spectroscopy. The ionic conductivity of the systems has been measured by using an LCR meter in a temperature ranging from 298 to 353 K. Maximum ionic conductivity of 1.58 × 10-4 S cm-1 at room temperature has been observed for the system of PVA-PEG-LiClO4-Al2O3 (50-25-15-10) with 15 wt% weight percent of LiClO4 salt in PVA-PEG blend matrix. The ac conductivity report indicates that the ionic conductivity of the PVA-PEG-LiClO4-Al2O3 complex is influenced by the concentration of LiClO4. The effect of temperature on the ionic conductivity of polymer electrolyte complexes has been estimated by changing the temperature ranging from 298 to 353 K. However, the conductivity of the nanofiber polymer electrolyte systems increases with the rise of temperature, and the maximum conductivity of 1.58 × 10-2 S cm-1 has been recorded at 353 K. The temperature-dependent conductivity follows the Arrhenius behavior.

Deciphering the Effect of Microstructural Modification in Sodium Alginate-Based Solid Polymer Electrolyte by Unlike Anions.

Microstructure modification in sodium alginate (NaAlg)-based solid polymer electrolytes by the perchlorate (ClO4-) and acetate (CH3COO-) anions of sodium salts has been reported. ClO4- participates in the structure-breaking effect via inter/intramolecular hydrogen bond breaking, while CH3COO- changes the amorphous phase, as evident from X-ray diffraction studies. The larger size and negative charge delocalization of ClO4- have a plasticizing effect, resulting in a lower glass transition temperature (Tg) compared to CH3COO-. Decomposition temperature is strongly dependent on the type of anion. Scanning electron microscopy images showed divergent modifications in the surface morphology in both electrolyte systems, with variations in salt content. The mechanical properties of the NaAlg-NaClO4 electrolyte systems are better than those of the NaAlg-CH3 COONa system, indicating weak interactions in the latter. Although most of the studies focus on the cation influence on conductivity, the interaction of the anion and its size certainly have an influence on the properties of solid polymer electrolytes, which will be of interest in the near future for sodium ion-based electrolytes in energy storage devices.

Polyampholyte saturated with simulated-body-fluid as a flexible, stretchable and self-healing gel electrolyte for biocompatible energy storages and capacitive circuit elements

As implantable electronic medical devices (IEMDs) develop, biocompatible polymer materials with body-friendly non-toxic nature are receiving great amount of attention. Polyampholyte hydrogels have mechanical flexibility and self-healing properties, as well as biocompatibility; thus, it can be applied in various implantable medical devices and wearable devices. In this study, the possibility of using a polyampholyte hydrogel saturated with simulated body fluid (PA-SBF) as the gel polymer electrolytes for energy storage devices and capacitive circuit elements of IEMDs is investigated. At the normal body temperature (35 °C), the PA-SBF exhibited high ionic conductivity of 17.6 mS cm−1 with negligible electron leakage. The supercapacitor fabricated with the PA-SBF gel electrolyte sandwiched between carbon-based electrodes showed an excellent areal capacitance of 219.6 mF cm−2 with a maximum potential window of 1.6 V. The self-healing properties and cytotoxicity of the PA-SBF gel electrolytes were examined as well. With high performance, flexibility, and self-healing property, the biocompatible PA-SBF gel electrolyte can be considered as a promising candidate for the electrolyte of electrochemical devices, energy sources and capacitive circuit elements of future IEMDs.

Novel nanocomposites based on Tetrazine liquid crystals for energy storage application

Polymethyl methacrylate (PMMA) /Tetrazine liquid crystal (LCTZ12) nanocomposites with different CNTs loadings have been prepared. The prepared nanocomposites were characterized using polarizing light microscope (POM), differential scanning calorimetry (DSC), Fourier transform Infrared Spectroscopy (FTIR) and broadband dielectric spectroscopy (BDS) in the range 10-1-106 Hz respectively. The most commonly observed texture of soft crystal phases was that of a mosaic pattern, as revealed by the POM technique. PMMA alone does not change the polarization states and appeared as isotropic material, but once LCTZ12 is added, crystal growth could be clearly noticed in the needle pattern inside the polymer matrix to compose an amazing structure of soft crystal G texture. The increase of LCTZ12 to about 20 wt% in the PMMA matrix led to more heterogeneous aggregation of liquid crystalline molecules. This ratio addition is enhancing of network connections inside the PMMA. Moreover, the dispersion of carbon nanotubes mounted on catalysts is found to accumulate in segregations in PMMA/ LCTZ12 nanocomposites. However, the location of CNTs is concentrated at bottom of polymer network due to the large difference in densities of LCs, PMMA, and CNTs. DSC is in agreement with the POM result of LCTZ12, which has multi soft crystals or highly self-assembled ordered liquid crystal phases near to room temperature. The FTIR proved that blend PMMA/ LCTZ12 (80/20) has a dramatic increase in the 1387 cm−1 peak of C = C as a response of the rise in the concentration or number of aromatic rings. Additionally, the vibrational scissoring peak located at 1477 cm−1 of methylene CH2 groups is increased significantly and C–H stretching in aliphatic regions at 2850 cm−1 and 2990 cm−1 as well. However, there is no significant change observed after CNTs addition to the PMMA/ 20 wt% LCTZ12 matrix. Regarding dielectric results, it was found that, the polymer dispersed liquid crystals PDLC system composed of (PMMA/20 wt% LCTZ12) possesses the most promising dielectric properties, that is; high dielectric permittivity with low losses compared to the other ratios. The addition of CNTs results in more localization of charge carriers along with mobile ions, causing higher ionic conductivity. The conductivity ranges altered from 3.2 × 10-10 S/cm in pure PDLC system to become 1.7 × 10-3 S/cm for PDLC doped with 10 wt% CNTs nanocomposite. The electrical energy density measurements for 3,6-bis(5-(Dodecyloxy) pyridin-2-yl)-1,2,4,5-tetrazine (LCTZ12) liquid crystals with 6 cationic centers in polymeric matrices proved to be suitable for flexible and efficient electrolytes for energy storage devices.

Magnesium ion conducting biopolymer blend-based electrolyte for energy storage application: Electrochemical characteristics

A casting technique was employed to produce plasticized magnesium ion conducting biopolymer blend electrolytes. Chitosan (CS) and polyvinyl alcohol (PVA) were used to deliver polymer blends, and 50 wt.% of magnesium nitrate (Mg(NO3)2) was incorporated as the source for Mg2+ ions supply. The CS:PVA:Mg(NO3)2 system was subjected to different concentrations of glycerol plasticizer to improve its ion conductivity. To assess their suitability as energy storage materials, the electrochemical characteristics of the fabricated films were examined employing broad methodologies. Distinguished improvement in dielectric constant was observed upon increasing plasticizer concentration. The appearance of relaxation peak in tanδ-M'' spectra and their asymmetric shape reveals the non-Debye relaxation process. The biopolymer blend electrolyte, with a plasticizer content of 55 wt.%, exhibited the highest DC conductivity, measuring 7.34 × 10−5 S.cm−1. In terms of potential stability, linear sweep voltammetry (LSV) analysis revealed a value of 2.34 V for this particular electrolyte. A non-Faradaic (capacitive) response to cyclic voltammetry (CV) is displayed, and there is no redox peak. The selected scan rate influenced the shape of the CV curves. When scan rates of 20 mV/s and 100 mV/s were employed, specific capacitance values of 5.41 and 16.46 F/g were determined. The stability of an electrochemical double-layer capacitor, which serves as an energy storage device, was evaluated by employing a charging-discharging technique and the electrode separator made of the most conducting sample. The results show promise for the potential application of the current plasticized magnesium ion-conducting biopolymer blend electrolyte in energy storage devices.

Ultrasound assisted lignin-decorated MWCNT doped flexible PVA–Chitosan composite hydrogel

This study reports a facile ultrasound-assisted synthesis and characterization of physically-crosslinked polyvinyl alcohol (PVA)-chitosan conductive hydrogels with lignin-decorated multi-walled carbon nanotube (MWCNT) as nanofiller. Homogeneous dispersion of MWCNT in the hydrogel matrix was achieved through the addition of lignin nanoparticles (optimum LP:MWCNT ratio of 2:1) in presence of acetone, followed by sonication of the mixture. FETEM images reveal lignin particles adhere onto the surface of the MWCNT, which assists de-agglomeration and dispersion of MWCNT in the aqueous medium. The hydrogels produced were mechanically stable and flexible in nature. The elastic moduli (G′) of hydrogels with 0.5 and 1 wt% MWCNT were 11170 and 11757 Pa, respectively, whereas the tensile strengths were 2.22 and 2.56 MPa. Further, addition of lignin (1 and 2 wt%) and MWCNT (0.5 and 1 wt%) imparted thermal stability to PVACS hydrogels. FESEM images confirmed the porous internal structure of the hydrogel with mesh size ∼7 nm for 1 wt% MWCNT content. The hydrogel with 1 wt% MWCNT possessed the highest conductivity (8.22 mS cm−1) among all the other hydrogels. These hydrogels have potential applications as electrodes or electrolytes for energy storage devices, ECG electrodes, and flexible sensors.

Energetically preferred Li+ ion jump processes in crystalline solids: Site-specific hopping in β-Li3VF6 as revealed by high-resolution 6Li 2D EXSY NMR

The visualization of atomic or ionic jump processes on the Ångström length scale is important to identify the preferred diffusion pathways in solid electrolytes for energy storage devices. Two-dimensional high-resolution 6Li nuclear magnetic resonance (NMR) spectroscopy is highly suited to yield unprecedented site-specific insights into local Li+ exchange processes within a single measurement. Here, the beta-modification of Li3VF6 is used as a model system for such an investigation as it provides a range of important Li+ geometric environments in one and the same crystal structure useful to elucidate qualitatively a ranking of energetic preferences of the Li+ exchange processes. In Li3VF6 the Li+ ions are subject to diffusive exchange processes among five crystallographically and magnetically inequivalent Li sites: LiFn (n = 6, 4). By using a sample with a natural concentration of the 6Li isotope, we suppressed unwanted spin-diffusion processes and visualized the various exchange processes on the ms time scale. We were able to verify the following ranking experimentally: Li+ ion jumps between face-shared polyhedra are preferred, followed by Li+ exchange between edge-shared configurations for which interstitial sites are needed to jump from site to site. Surprisingly, Li+ exchange between corner-shared polyhedra and Li+ hopping involving almost isolated LiF4 polyhedra do contribute to overall Li+ self-diffusion as well. In this sense, the current study experimentally verifies current predictions by theory but also extends our understanding of ion dynamics between corner-shared Li-bearing polyhedra.

Self-Healing, Flexible and Smart 3D Hydrogel Electrolytes Based on Alginate/PEDOT:PSS for Supercapacitor Applications.

Hydrogel electrolytes for energy storage devices have made great progress, yet they present a major challenge in the assembly of flexible supercapacitors with high ionic conductivity and self-healing properties. Herein, a smart self-healing hydrogel electrolyte based on alginate/poly (3,4-ethylenedioxythiophene):poly(styrenesulfonate) (alginate/PEDOT:PSS)(A/P:P) was prepared, wherein H2SO4 was employed as a polymeric initiator, as well as a source of ions. PEDOT:PSS is a semi-interpenetrating network (IPN) that has been used in recent studies to exhibit quick self-healing properties with the H₂SO₃ additive, which further improves its mechanical strength and self-healing performance. A moderate amount of PEDOT:PSS in the hydrogel (5 mL) was found to significantly improve the ionic conductivity compared to the pure hydrogel of alginate. Interestingly, the alginate/PEDOT:PSS composite hydrogel exhibited an excellent ability to self-heal and repair its original composition within 10 min of cutting. Furthermore, the graphite conductive substrate-based supercapacitor with the alginate/PEDOT:PSS hydrogel electrolyte provided a high specific capacitance of 356 F g-1 at 100 mV/s g-1. The results demonstrate that the A/P:P ratio with 5 mL PEDOT:PSS had a base sheet resistance of 0.9 Ω/square. This work provides a new strategy for designing flexible self-healing hydrogels for application in smart wearable electronics.

Effect of boron-based glass additives on the ionic conductivity of Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a promising candidate as the solid electrolyte in energy storage devices. For practical considerations, the most common ways to ameliorate the low density and high ionic resistance of LATP are usually to use glass additives. In this work, the boron-based (B2O3, B2O3-SiO2-PbO (BSP), and B2O3-SiO2-K2O-Al2O3 (BSKA)) glass are added into LATP by solid method. As the results, the main diffraction peaks of all prepared samples maintain the NASICON-type with the R-3c space group. Meanwhile, the symmetric stretching vibrations of O-P-O bands is redshifted with the addition of boron-based glass, which plays a positive role in bulk conductivity. Additionally, the introduction of boron-based glass additives is effective to increase the grain sizes of the LATP samples. The relative density of the sample is obtained from 93.37% to 95.42%. Furthermore, the total conductivities of 1.33 × 10−4, 1.37 × 10−4, 1.97 × 10−4 S cm−1 are obtained in ceramic samples after B2O3, BSP and BSKA glass additives adding, respectively. The activation energy shows a reduction of 5.26% to 0.36 eV after BSP and BSKA glass adding. Satisfactorily, B2O3, BSP and BSKA glass have a certain influence on the conductivity, and bear a more favorable argument for the regulation of the morphology and density in the future.

A universal approach for predicting electrolyte decomposition in carbon materials: On the basis of thermodynamics

A new methodology based on thermodynamic theorem is introduced and tested here to describe electrochemical side reactions of nonaqueous-based electrolytes in energy storage devices. The reactions are most likely to be triggered by carbon materials that contains active sites including metal atoms and crystalline defects. As an example, decomposition reactions of a widely-used solvent for nonaqueous electrolytes, propylene carbonate (PC), are discussed in detail. Mechanisms and equilibrated electrode potentials of PC decomposition are predicted by generalized computational hydrogen electrode approach, which agrees well with experimental results. Li, Na, K, Mg, Ca, Ti, Cr, Fe, Ni, Mo atoms tethered by single and double vacancy defects are found hazardous in energy storage devices including alkali metal ion batteries and electrochemical capacitors, for they can make PC decompose within the electrode potential window of these devices. Differences in key electronic and thermodynamic properties of studied metal elements are proposed as reactivity descriptors. Dominating contributions to reactivity of metal atoms are unveiled by data engineering. The methodology raised in this work provides broad impact for theoretically predicting side reactions in energy storage devices, and proves the accuracy of generalized computational approach in nonaqueous-based energy storage systems.

Brine Refrigerants for Low‐cost, Safe Aqueous Supercapacitors with Ultra‐long Stable Operation at Low Temperatures

AbstractTraditional aqueous energy storage devices are difficult to operate at low temperatures owing to the poor ionic conductivity and sluggish interfacial dynamics in frozen electrolytes. Herein, the low‐cost brine refrigerants for food freezing and preservation as electrolytes, and unexpectedly realize high ionic conductivity and stable operation of an aqueous storage device at low temperatures are demonstrated. A CaCl2 brine refrigerant electrolyte (BRE) with a low freezing point −55 °C and high ionic conductivity (10.1 mS cm−1 at −50 °C) is developed for supercapacitors (SCs), which retains 80% of the room temperature capacity at −50 °C and exhibits ultra‐long cycle life with excellent capacity retention of 92% over 98,500 cycles, outperforming the other SCs which can be operated below −40 °C in literature. Moreover, the SCs with MgCl2 and NaCl BREs can also be operated successfully with excellent cycle stability and high‐capacity retention at low temperatures of −30 and −20 °C, respectively. Fundamental correlation between various cations and their effect on the freezing point reduction of aqueous electrolytes is revealed via Raman investigation and molecular dynamics simulations. This study provides a rational design strategy for green, inexpensive, and safe low‐temperature aqueous electrolytes for energy storage devices.

Interfacial structures and decomposition reactions of hybrid anion-based ionic liquids at lithium metal surface from first-principles and ab initio molecular dynamics

Ionic liquids (ILs) based on hybrid anions have recently been investigated as appealing alternative electrolytes for energy storage devices, because such asymmetric anions have the potential to reduce melting point and inhibit crystallization of ILs without losing advantages found for the common symmetric ones. In this work, interfacial structures and decomposition reactions of the ILs consisting of two hybrid anions (FTFSI− and MCTFSI−) with the [BMP] cation at lithium metal surface were intensively studied using the combination of first-principles DFT calculations and ab initio molecular dynamics (AIMD) simulations. The corresponding ILs comprising the symmetric anions (TFSI− and FSI−) were also considered for comparison. The adsorption of the ILs on the surface is governed by the interactions between the anions and the substrate mainly via the Li−O bonds. For [BMP][FTFSI] rapid decomposition of the anion triggered by the S−F and S−N bond cleavage was observed, while the first reaction step for [BMP][MCTFSI] involves the breaking of the C−S and S−N bonds of the anion. Particularly, the differences of adsorption properties and reaction mechanisms for these two classes of ILs on the Li surface were demonstrated in detail.

Effect of nano TiO2 on the thransport, structural and thermal properties of PEMA-NaI solid polymer electrolytes for energy storage devices

Nano Titania (TiO2) added polymer electrolytes have been prepared successfully via conventional solvent casting technique using Poly (Ethyl Methacrylate) (PEMA) as the host polymer and Sodium Iodide (NaI) as salt. Different characterization techniques such as AC impedance spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy, X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), and Thermogravimetric differential thermal analysis (TG-DTA) have been employed. With the help of the AC impedance analyzer, the ionic conductivity for all samples has been calculated and higher ionic conductivity of 2.91 × 10−5 Scm−1 is achieved for the system PEMA/NaI/4 wt% TiO2 at room temperature. The shifting and disappearance of bands in FTIR spectroscopy confirm the mixing of polymer and salt in the homogeneous polymer electrolytes. The decrease in crystallinity and hence the increase in amorphous nature has been confirmed through XRD studies. The diffusion coefficient, mobility, and the number of mobile ion concentrations have been estimated for all compositions of nano TiO2 added PEMA/NaI systems. The thermal stability of the membranes has been investigated by TG-DTA analysis.

The effect of inorganic nanoparticles on ion conduction in poly(lithium acrylate)-based composite polymer electrolytes for energy storage devices

Recently, considerable researches are conducted to develop promising polymer electrolytes for Li-ion batteries (LIBs). Herein, we prepared poly(lithium acrylate) (PAALi)-based composite polymer electrolytes (CPEs) containing alumina (Al2O3) nanoparticles. The addition of inorganic nanoparticles into the PAALi matrix can not only improve CPE’s ionic conductivity ( at 303 K), but also enhance CPE’s mechanical properties due to the nanoparticles acting as cross-linkers between the PAALi chains. We systematically investigated the influences of inorganic nanoparticle types (pure alumina vs. vinyl functionalized alumina) and contents on ionic conduction and mechanical properties of PAALi-based CPEs.

Highly Stable and Eco-friendly Marine Self-Charging Power Systems Composed of Conductive Polymer Supercapacitors with Seawater as an Electrolyte.

A self-charging power system harvesting random and low-frequency wave energy into electricity provides a promising strategy for the construction of smart oceans. However, the system faces huge challenges of easy corrosion in the marine environment and the utilization of toxic organic electrolytes in energy storage devices. To address the issues above, a seawater supercapacitor (SWSC) for the marine self-charging power system is rationally proposed by using a conductive polymer, polypyrrole with hollow morphology (h-PPy), to enhance the stability and capacitance while using seawater as an eco-friendly electrolyte to reduce the cost and achieve sustainability. The hollow design provides a shortcut for the ion transportation of seawater into the h-PPy electrode, and the SWSC achieves a high power density of 4.32 kW kg-1 under an energy density of 5.12 W h kg-1. Even after 180 days in seawater, h-PPy still endows a mass retention of 99.9%, enabling the SWSC to maintain a stability of 99.3% after 6000 cycles. More importantly, when combined with a TENG module as the marine self-charging power system to harvest wave energy, the system provides a stable output in water wave to drive electronics and sensors, which shows a competitive potential in the smart ocean and marine internet of things.

Adhesive, free-standing, partially fluorinated comb copolymer electrolyte films for solid flexible supercapacitors

Solid-state electrolytes exhibiting high safety and flexibility have attracted global attention as an alternative to conventional fluidic and flammable liquid electrolytes for energy storage devices. Herein, we report a free-standing solid electrolyte film with high ionic conductivity, strong adhesive property, and good mechanical strength based on a partially fluorinated, microphase-separated comb copolymer consisting of superhydrophobic poly(2,2,2-trifluoroethyl methacrylate) and amphiphilic crystalline poly(ethylene glycol) behenyl ether methacrylate. The comb copolymer electrolyte film with ionic liquid (IL) exhibited a wide potential window of 2.2 V and retained its excellent flexibility up to 85 wt% IL loading. This property arises from the self-assembled microphase separation, which functions as an effective channel for ion transportation, resulting in improved ionic conductivity. The electrolyte film was applied to a solid supercapacitor with activated carbon electrodes, resulting in a high specific capacitance (37.3 F g−1), energy density (23.2 Wh kg−1), and power density (530 W kg−1), and outperformed the cells made with conventional poly(vinyl alcohol) electrolyte. Interestingly, the fabrication of supercapacitors did not require any separator, adhesive, or packaging process because of the strong self-adhesive and mechanical properties of the comb copolymer electrolyte film.

Promoting Persistent Superionic Conductivity in Sodium Monocarba-closo-dodecaborate NaCB11H12 via Confinement within Nanoporous Silica.

Superionic phases of bulk anhydrous salts based on large cluster-like polyhedral (carba)borate anions are generally stable only well above room temperature, rendering them unsuitable as solid-state electrolytes in energy-storage devices that typically operate at close to room temperature. To unlock their technological potential, strategies are needed to stabilize these superionic properties down to subambient temperatures. One such strategy involves altering the bulk properties by confinement within nanoporous insulators. In the current study, the unique structural and ion dynamical properties of an exemplary salt, NaCB11H12, nanodispersed within porous, high-surface-area silica via salt-solution infiltration were studied by differential scanning calorimetry, X-ray powder diffraction, neutron vibrational spectroscopy, nuclear magnetic resonance, quasielastic neutron scattering, and impedance spectroscopy. Combined results hint at the formation of a nanoconfined phase that is reminiscent of the high-temperature superionic phase of bulk NaCB11H12, with dynamically disordered CB11H12– anions exhibiting liquid-like reorientational mobilities. However, in contrast to this high-temperature bulk phase, the nanoconfined NaCB11H12 phase with rotationally fluid anions persists down to cryogenic temperatures. Moreover, the high anion mobilities promoted fast-cation diffusion, yielding Na+ superionic conductivities of ∼0.3 mS/cm at room temperature, with higher values likely attainable via future optimization. It is expected that this successful strategy for conductivity enhancement could be applied as well to other related polyhedral (carba)borate-based salts. Thus, these results present a new route to effectively utilize these types of superionic salts as solid-state electrolytes in future battery applications.